Complement fixation and indirect micro-immunofluorescence (IF) tests were compared for specificity and sensitivity in detection of antibodies against R-ickettsia conorii in acute and convalescent human sera. Purified particulate rickettsial antigens were used. Good agreement between these 2 tests was found. Use of specific anti-Ig[immunoglobulin]G and anti-IgM sera in parallel IF tests enabled differentiation between recent and past infections.